The present invention relates to a safety brake for a load receiving means of an elevator, with a fixing means which can be brought into a locked and an unlocked state and which in the locked state fixes the load receiving means to a rail, as well as a method for unlocking such a safety brake after a braking process.
Safety brakes are used with a number of different operating principles. A large portion thereof have a clamping mechanism which, after activation by a speed limiter system, produces a clamping action between components of the safety brake and at least one stationary rail, which is mounted parallel to the travel path of the load receiving means, with use of the kinetic energy of the moving load receiving means. Due to self-locking in the clamping mechanism, some of these safety brakes can be unlocked again after the braking process only with considerable expenditure of force.
A safety brake of the kind stated in the foregoing is known from patent document EP 0 899 231 A1 and is explained in more detail in the description below with reference to FIG. 2.
In order to unlock safety brakes, which have a self-locking clamping mechanism, after a braking process, these have to be moved against the movement direction present before the braking process, which usually happens by moving the load receiving means. Such a movement is usually produced by lifting the load receiving means by the drive unit of the elevator or by lowering the load receiving means by the drive unit with utilization of the weight force of the load receiving means and possibly an additional load. For overcoming the mentioned self-locking of the clamping mechanism there is needed a displacement force which is substantially increased by comparison with normal operation. This increased displacement force in many cases exceeds the available force of the drive unit or the weight force of the load receiving means. Unlocking by manipulation at the safety brake is usually not possible, since in the case of braking this is not accessible.
The present invention has the object of creating equipment by which unlocking of such safety brakes is made possible with substantially reduced release force, i.e. by exclusive use of the unassisted drive unit of the elevator or the weight force of the load receiving means.
The advantages achieved by the invention are essentially that simple and economic safety brakes, which need to overcome substantial frictional forces for unlocking thereof, are usable without the drive units having to apply more than the lifting force required for normal operation and without the load receiving means having to be loaded with additional loads for unlocking after a braking process from an upward movement.
In order, for unlocking the safety brake with the assistance of the abutments movable relative to the fixing means, to be able to exert a blow or impact on these fixing means, these abutments are expediently fixedly connected with the load receiving means so that the blow can be produced by simple vertical movement of the load receiving means.
The fixing means is preferably so connected with the load receiving means that it is displaceable relative to the load receiving means parallel to the stationary rail within a limited displacement path, wherein the abutments form the limitation of this displacement path. For unlocking the safety brake after a braking process the load receiving means can thereby be moved and accelerated over a limited displacement path, without hindrance by the fixing means fixedly seated on the rail, before one of the abutments fixedly connected with the load receiving means collides with this fixing means and unlocks this by a blow utilizing the kinetic energy of the moved load receiving means.
In a further preferred embodiment of the invention at least one of the abutments forming the limitations of the displacement path is adjustable, for example in the manner that the limitation consists of an abutment screw with a fixing nut. The displacement path can thus be optimized in correspondence with the prevailing conditions.
The fixing means is, with advantage, held in normal operation by at least one spring element in contact with the abutment forming the upper limitation of the displacement path and connected with the load receiving means, wherein this spring element has to compensate for at least the weight force of the fixing means. By this measure it is avoided that in the case of a braking process from a downward movement of the load receiving means, in which the greatest braking forces arise, the fixing means firmly clamped to the stationary rail collides against the said upper abutment like a hammer. On unlocking of the safety brake through lifting the load receiving means by the drive unit of the elevator, the load receiving means moves upwards relative to the fixing means, which is fixedly seated on the stationary rail, and against the spring force until an abutment forming the lower limitation of the displacement path collides with the fixing means and thereby helps to unlock the clamping mechanism thereof.
It is advantageous to achieve the limited displaceability of the fixing means relative to the load receiving means in such a manner that the two components are connected together by way of linear guides or pivot guides. Collar screws in guide slots, dovetail or prismatic sliding guides, parallelogram linking lever guides or parallelogram leaf spring guides are suitable forms of embodiment for that purpose.
Displacement paths having a length limited to 5 to 30 mm have proved advantageous for the different conditions of use and variants of safety brakes.
For elevators that have a counterweight and in which a safety brake has to secure the load receiving means even before excess speed in an upward direction it is advantageous to use a fixing means which is effective as a unit in both directions of movement of the load receiving means, wherein different braking forces can be generated for the downward direction and the upward direction. For elevators without a counterweight, fixing means which function only in the downward direction of the load receiving means are sufficient.
The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which:
FIG. 1 is a schematic illustration of an elevator with a safety brake according to the present invention;
FIG. 2 is a schematic illustration of an embodiment for a fixing means effective in both directions of travel of the load receiving means;
FIG. 3 is a schematic illustration of another embodiment for a fixing means effective only in the downward direction of travel of the load receiving means;
FIG. 4 is a schematic illustration of the safety brake according to the present invention after a braking process from a downward movement of the load receiving means;
FIG. 5 is similar to FIG. 4 and shows the safety brake at the instant of the unlocking process, and
FIGS. 6, 7 and 8 are each a side elevation and top plan view of alternate embodiments of the safety brake with different solutions for realization of the displaceability of the fixing means.